1. Field
Example embodiments relate to light-sensing apparatuses, methods of driving the light-sensing apparatuses, and optical touch screens including the light-sensing apparatus.
2. Description of the Related Art
An oxide semiconductor transistor is a transistor that uses an oxide semiconductor as a material for a channel. For example, an oxide semiconductor transistor may include a substrate, a gate disposed on the substrate, a gate insulating layer disposed on the substrate and the gate so as to cover a surrounding region including the gate, a channel layer formed of the oxide semiconductor and disposed on the gate insulating layer, and a source and a drain that are disposed to cover ends of the channel layer.
The oxide semiconductor transistor may be light-sensitive according to a material of the oxide semiconductor which is used as the channel layer. For example, oxide semiconductor materials which are light-sensitive may include a ZnO-based oxide semiconductor (e.g., ZnO, TaZnO, InZnO(IZO), GaInZnO(GIZO), and the like). In a case where a light sensitive oxide semiconductor material is used as a channel layer, the oxide semiconductor transistor may be used as a light-sensing device due to a characteristic that a threshold voltage and a drain current change according to a wavelength or an amount of an incident light. Due to the aforementioned characteristic, the oxide semiconductor transistor may replace a photodiode having a PN-junction structure which is widely used as a light-sensing device.
In particular, because an oxide semiconductor transistor may generate a larger photocurrent than a photodiode, if an oxide semiconductor transistor is used as the light-sensing device, it is possible to omit a capacitor that is generally used in a light-sensing pixel to accumulate photocurrent generated charges over a period of time. For example, the light-sensing pixel may include an oxide semiconductor transistor for sensing light and a switching transistor for outputting data. Thus, the oxide semiconductor transistor may be used in various apparatuses that sense light, for example, an image-capturing apparatus, an optical touch screen panel, and the like.
However, in an oxide semiconductor transistor that uses an oxide semiconductor as the material for the channel, due to stress caused by light and electricity, a threshold voltage is increasingly shifted in a negative voltage direction over time. In particular, as light-sensitiveness of the material for the channel increases, a threshold voltage shift in the negative voltage direction further increases. When the threshold voltage of the oxide semiconductor transistor is shifted in the negative voltage direction, the oxide semiconductor transistor may not normally perform ON/OFF operations, which may deteriorate an operational reliability of an apparatus that uses the oxide semiconductor transistor.